Understanding the Causes of Canker Sores and the Role of SLS

By S. C. Aris — about the author

Last updated: 2026-05-01

What Causes Canker Sores? Canker sores, or recurrent aphthous stomatitis, are primarily caused by factors such as stress, nutritional deficiencies, and potential irritants like sodium lauryl sulfate (SLS). SLS, a common ingredient in toothpaste, can trigger irritation in sensitive individuals by disrupting the mucosal barrier, similar to weakening a protective shield. Research by Alli BY et al. (2019) highlights how SLS can exacerbate these oral ulcers in some people.

Key Considerations:

1. Biological Irritation: SLS may cause irritation by affecting the integrity of the mucosal barrier, akin to a loss of structural integrity in a protective wall (Alli BY et al., 2019).
2. Individual Sensitivity: The sensitivity to SLS varies, and while some individuals may not experience any adverse effects, others with predispositions to oral ulcers may find their symptoms aggravated (Shim YJ et al., 2012).
3. Alternative Factors: Besides SLS, canker sores can also be linked to stress and deficiencies in vitamins like B12, folate, and iron, which play crucial roles in maintaining oral health.

What Causes Canker Sores: The Role of Immune Response

Canker sores, or aphthous ulcers, are primarily linked to an overactive immune response. When your body's defenses mistakenly attack the cells in your mouth, it results in painful, small ulcers. This process is known as autoimmune inflammation. Imagine this like a security system that's too sensitive, triggering alarms even when there's no real threat. Research by Alli BY et al. (2019) indicates that this immune misfire can be exacerbated by various factors, including stress and nutritional deficiencies.

• The Science: Autoimmune inflammation. The immune system attacks healthy tissue in the mouth, causing ulcers. Studies confirm that stress and diet can worsen this response (Alli BY et al., 2019).
• What the Studies Show: A heightened immune response is a key factor in canker sore development, with stress being a significant aggravator.

Sodium Lauryl Sulfate (SLS) and Oral Health

Sodium Lauryl Sulfate (SLS) is a common ingredient in many oral care products, known for its foaming properties. However, it can irritate the mucous membranes in some individuals, potentially leading to canker sores. This irritation occurs through a process called chemical irritation, where SLS disrupts the natural protective layer of the oral mucosa. Think of it as a mild abrasive that strips away your mouth's natural defenses. Studies by Sabri H et al. (2023) have explored the dual nature of SLS, noting both its benefits and its potential to irritate sensitive oral tissues.

• The Science: Chemical irritation. SLS can disrupt the protective barrier in the mouth, leading to irritation. Research indicates a correlation between SLS exposure and increased irritation (Sabri H et al., 2023).
• What the Studies Show: While SLS is effective in cleaning, its potential to cause irritation in sensitive individuals cannot be ignored.

Genetic Predisposition and Canker Sores

Genetics play a significant role in determining who might be more susceptible to canker sores. This is largely due to inherited variations in immune response and inflammatory pathways. Genetic susceptibility can be likened to inheriting a blueprint that predisposes one to certain conditions. Research by Horita K et al. (2017) has shown that individuals with a family history of canker sores are more likely to experience them themselves.

• The Science: Genetic susceptibility. Inherited traits can predispose one to autoimmune conditions like canker sores. Studies highlight a strong familial link (Horita K et al., 2017).
• What the Studies Show: Family history is a strong predictor of canker sore occurrence, emphasizing the role of genetics.

Dietary Triggers and Nutritional Deficiencies

Diet significantly influences the occurrence of canker sores. Certain foods can trigger these ulcers by causing irritation or an allergic reaction. Additionally, deficiencies in essential nutrients like vitamin B12, zinc, and iron can impair the body's ability to maintain healthy oral tissues, leading to ulcer formation. This is a case of nutritional insufficiency, where the lack of key nutrients weakens the body's defenses. While no specific study from the approved list directly links diet to canker sores, this is a widely recognized factor in the broader scientific community.

• The Science: Nutritional insufficiency. Deficiencies in key vitamins and minerals can lead to weakened oral health. While specific studies are not cited, this is a well-acknowledged aspect of canker sore development.
• What the Studies Show: Maintaining a balanced diet rich in essential nutrients is crucial for preventing canker sores.

The Other Side of the Debate: SLS's Dual Role

While some research highlights the potential for SLS to irritate the oral mucosa, other studies, such as those by Kasi SR et al. (2022), suggest that its role in oral hygiene is beneficial when used appropriately. The debate centers around balancing its effective cleaning properties with the risk of irritation. This dual role of SLS can be seen as a double-edged sword, where its benefits must be carefully weighed against its potential to cause harm, particularly in those with sensitive oral tissues.

• The Science: Dual role of SLS. While it cleans effectively, it can cause irritation. Studies highlight this balance (Kasi SR et al., 2022).
• What the Studies Show: The use of SLS in oral care products remains a topic of debate, with a focus on minimizing irritation while maximizing cleaning efficiency.

How to Manage Canker Sores

1. Identify Triggers. Keep a diary of foods and activities to pinpoint what might be causing your sores.
2. Choose the Right Products. Opt for SLS-free toothpaste and consider lipid-based oral care solutions.
3. Maintain a Balanced Diet. Ensure adequate intake of vitamins and minerals to support oral health.

Frequently Asked Questions

What causes canker sores?

Canker sores, or aphthous ulcers, are often caused by factors such as stress, nutritional deficiencies, and certain food sensitivities. The exact mechanism is not fully understood, but it's believed to involve an immune response that damages the mucosal lining in the mouth. This response can be triggered by minor injuries or irritants.

Is sodium lauryl sulfate (SLS) linked to canker sores?

Yes, sodium lauryl sulfate (SLS), a common ingredient in toothpaste, has been linked to canker sores in some individuals. Research indicates that SLS can lead to mucosal irritation, potentially increasing the risk of developing these ulcers (Alli BY et al., 2019). This happens because SLS can disrupt the protective mucous layer in the mouth, acting like a chemical interference that weakens the tissue.

How does stress contribute to canker sores?

Stress is known to contribute to the development of canker sores through a process called immunomodulation. Stress can alter the immune system's function, making it more likely to attack the mucosal cells lining the mouth. This can result in the formation of painful ulcers.